The invention refers to a protective structure, in particular for use with a machine tool or similar work unit.
In particular, the object of the invention is a protective structure of the type referred to as a "roller blind", designed to screen determined portions of a work unit of any type.
The prior art protection structures of the above-mentioned type, frequently viable on foot with the aim of offering accident protection and hygienic work conditions to the operator, are usually used to screen areas of work units which must be accessible rapidly and automatically, both for functional reasons and for maintenance, and essentially comprise a flexible wall, which will be defined hereinafter as a "blind" for the sake of brevity, which blind is defined, for example, by a plurality of slats positioned in line and reciprocally non-rigidly constrained, for example by hinging with rotation possibility.
In their most pertinent embodiment, in the present invention the blinds develop along a plane and run along appropriate guide means. Taking for example blinds which are destined to close the upper floor of a pit for machines or work units in which the base or sliding plane of the upright of the mobile operating element is below the said unit access plane or upper floor, the two tracts of blind which develop along the said upper floor are connected by the opposite ends of the operating element which is able to move in the two senses according to the longitudinal development direction of the blind tracts themselves. The end portions of each blind are wound on respective elongated substantially cylindrical support elements, for example rollers. During the course of the movements in one sense or the other of the mobile operator element, the two tracts of blind vary their lengths, winding partially on to the relative elongated support elements or respectively partially unwinding from them.
In some cases the said elongated support means are connected to respective motor means able to produce a sliding in the two senses of the blind tracts, with consequent opposite variations in the quantity of blind respectively wound on one and the other of the elongated support elements. Alternatively, the elongated support means or rollers are not motorised, and instead are equipped with respective pre-loaded spiral springs which, while the blind runs in one direction or the other, drawn by the above-mentioned mobile operator element, are respectively either loaded or unloaded. Consequently, each time that the blind is moved in one sense or in the other with respect to a neutral position in which the said springs are loaded equally, when the motor direction is inverted the more loaded of the springs tends to ease the return of the blind itself towards the neutral position.
Obviously, the protective structures in which the said elongated support means are motorised are considerably expensive, since, apart from having the said motorised means, they imply the presence of complicated electronic switchboards able to regulate the activity of the motor means themselves.
Specifically, protective structures equipped with rollers with preloaded spiral springs give rise to another kind of drawback, particularly serious in the cases in which the said springs are part of work units equipped with mobile operating elements, connected to the said blinds, which elements must be able to reach and maintain at every moment very precise positions. When the blinds are not occupying the said neutral position the springs exert respectively different traction forces on the blinds themselves, with consequent subjecting of the mobile operating elements to non-zero resulting forces which vary its position. A common drawback of both the prior art solutions examined consists in the fact that the sliding of the blinds within the predetermined guides creates problems of noise, caused by considerable friction originating from the said sliding.
The aim of the present invention is thus that of eliminating the above-mentioned drawbacks.
In particular, one important aim of the present invention is that of providing a protective structure of the above-mentioned type which is simple and economical and does not influence negatively the functioning of the work unit incorporating the protective structure itself.